This invention relates to concrete structural elements, methods of fabricating them and buildings using them.
One class of concrete structural element is called a concrete sandwich panel. It is composed of two layers, called wythes, of concrete separated by a layer of insulation. The concrete wythes are connected together through members that pass through the insulation into the concrete layers and transmit forces between the two.
In one type of prior art precast concrete sandwich panel of this class, forces are transmitted between the two concrete layers by metal trusses. These trusses are capable of transmitting force in a number of different directions such as perpendicular to the planes of the concrete layers or at angles to those planes but in the plane of the metal trusses.
The precast concrete sandwich panels which utilize metal trusses that pass through the insulation layer and are embedded in the concrete layers to hold the concrete layers together have a disadvantage in that the metal struts of the truss readily transfer heat from one concrete layer to the other through the metal. Thus there is a low resistance heat transfer path throughout the entire sandwich panel.
In another prior art type of sandwich panel, straight plastic pins are forced through the top layer of concrete, the insulative layer and into the bottom layer. They are shaped so as to be embedded and fastened to the two concrete layers and transmit forces between them. In one prior art embodiment, they are at an angle slanting downwardly so as to transmit some downward force. These panels provide good insulation between the two concrete layers.
The precast concrete sandwich panels which utilize straight plastic pins have a disadvantage in that they are not true composite panels which can transmit large vertical forces at both obtuse and acute angles to the plane of the panels with a structural outer concrete layer as they are implemented in practice. Thus, while they have better thermal insulating characteristics than the precast concrete sandwich panels in which the concrete wythes are connected by metal trusses, they have poor force transmitting characteristics.